Honeycomb-shaped ceramic separation-membrane structure

ABSTRACT

There is provided a honeycomb-shaped ceramic separation-membrane structure having higher pressure resistance than conventional ones and being capable of reducing production costs. The honeycomb-shaped ceramic separation-membrane structure ( 1 ) is provided with a honeycomb-shaped base material ( 30 ), an intermediate layer, and a separation layer. At least part of a ceramic porous body ( 9 ) has a structure where aggregate particles are bonded to one another by an inorganic bonding material component. In the ceramic separation-membrane structure ( 1 ), an internal pressure fracture strength capable of fracturing the structure by application of water pressure inside the cells ( 4 ) is 7 MPa or more.

TECHNICAL FIELD

The present invention relates to a honeycomb-shaped ceramicseparation-membrane structure having pressure resistance.

BACKGROUND ART

In recent years, there has been used a ceramic filter in order toselectively collecting only a specific component from a mixture (mixedfluid) of many components. Since a ceramic filter is superior to anorganic polymer filter in mechanical strength, durability, corrosionresistance, and the like, it is preferably applied to removal ofsuspended substances, bacteria, dust, and the like in liquid or gas inthe wide fields of water treatment, exhaust gas treatment, medicine,food, etc.

In such a ceramic filter, it is necessary to make the membrane area(area of the separation membrane) large in order to improve waterpermeability with securing the separation performance, and, for thepurpose, it is desirable to have a honeycomb shape. Furthermore, ahoneycomb-shaped filter (honeycomb-shaped ceramic separation-membranestructure) has advantages of being hardly broken and cost saving incomparison with a tube-typed filter. In many cases, a honeycomb-shapedceramic separation-membrane structure has a circular columnar externalshape and is provided with a porous base material having a large numberof parallel flow passages (referred to as cells) formed in the axialdirection of the structure inside the structure. Furthermore, aseparation membrane having small pore diameter in comparison with theporous base material is formed on the inside wall faces forming thecells.

In the honeycomb-shaped ceramic separation-membrane structure (precisefiltration membrane, ultrafiltration membrane, pervaporation membrane,gas separation membrane, and reverse osmosis membrane), it is desirableto increase the permeation flow rate by applying high pressure uponoperation. In particular, in ultrafiltration, gas separation, and areverse osmosis membrane, since the permeation coefficient of theseparation membrane is small, it is necessary to perform separation andrefinement with applying high operating pressure. The Patent Document 1reports a pressure resistant zeolite separation membrane having azeolite membrane thickness of 0.5 to 30 μm.

The Patent Document 2 discloses a cross-flow filtration device having animproved permeation flow rate.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: JP No. 3128517-   Patent Document 2: JP-B-6-016819

SUMMARY OF THE INVENTION

However, a conventional honeycomb-shaped ceramic separation-membranestructure may be fractured under an operation pressure of 5 MPa or more.In addition, when the porous base material is a self-sintering type asin the Patent Document 1, the firing temperature is high, and it causeshigh costs. Though the shape of the separation membrane is specifiedfrom the viewpoint of the permeation flow amount in the Patent Document2, there is no particular description regarding strength.

The present invention aims to provide a honeycomb-shaped ceramicseparation-membrane structure having higher pressure resistance thanconventional ones and being capable of reducing production costs.

It was found out that the aforementioned problem can be solved byallowing the separation membrane structure to be provided with anintermediate layer and allowing at least part of the ceramic porous bodyto have a structure where aggregate particles are bonded to one anotherby an inorganic bonding material component. That is, according to thepresent invention, there is provided a honeycomb-shaped ceramicseparation-membrane structure having an internal pressure fracturestrength of 7 MPa or more when the structure is fractured upon applyingpressure to the inside of the cells.

[1] A honeycomb-shaped ceramic separation-membrane structure comprising:a honeycomb-shaped base material having partition walls of a ceramicporous body having a large number of pores formed therein and aplurality of cells formed by the partition walls and functioning aspassages for a fluid passing through the ceramic porous body, anintermediate layer of a ceramic porous body having a large number ofpores having a small average pore diameter in comparison with a surfaceof the base material and being disposed on the surface of the basematerial, and a separation layer disposed on a surface of theintermediate layer; wherein at least a part of the base material and theintermediate layer has a structure where aggregate particles are bondedto one another by an inorganic bonding material component, and aninternal pressure fracture strength fracturing the structure whenpressure is applied to the inside of the cells is 7 MPa or more.

[2] The honeycomb-shaped ceramic separation-membrane structure accordingto [1], wherein the intermediate layer thickness, which is the thicknessof the intermediate layer, is 150 μm or more and 500 μm or less.

[3] The honeycomb-shaped ceramic separation-membrane structure accordingto [1] or [2], wherein the base material thickness excluding theintermediate layer and the separation layer at the shortest portionbetween the cells is 0.51 mm or more and 1.55 mm or less.

[4] The honeycomb-shaped ceramic separation-membrane structure accordingto any one of [1] to [3], wherein the proportion of an inorganic bondingmaterial component in an inorganic solid content of the intermediatelayer is 26% by mass or more and 42% by mass or less.

[5] The honeycomb-shaped ceramic separation-membrane structure accordingto any one of [1] to [4], wherein the aggregate particles of the basematerial and the intermediate layer are one selected from the groupconsisting of alumina, titania, mullite, powder of potsherd, andcordierite, and the inorganic bonding material of the base material andthe intermediate layer is one selected from the group consisting ofsinterable alumina, silica, glass frit, clay mineral, and sinterablecordierite.

[6] The honeycomb-shaped ceramic separation-membrane structure accordingto any one of [1] to [5], wherein the base material has an average poresize of 5 to 25 μm, and the intermediate layer has an average pore sizeof 0.005 to 2 μm.

[7] The honeycomb-shaped ceramic separation-membrane structure accordingto any one of [1] to [6], which is a gas separation membrane used forgas separation.

[8] The honeycomb-shaped ceramic separation-membrane structure accordingto any one of [1] to [7], wherein the separation layer is formed ofzeolite.

[9] The honeycomb-shaped ceramic separation-membrane structure accordingto [8], wherein the separation layer is formed of DDR type zeolite.

[10] The honeycomb-shaped ceramic separation-membrane structureaccording to [9], which is a gas separation membrane used forselectively separating carbon dioxide.

A honeycomb-shaped ceramic separation-membrane structure of the presentinvention has an internal pressure fracture strength of 7 MPa or moreand high fracture strength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a part cut out, showing an embodiment ofa ceramic separation-membrane structure of the present invention.

FIG. 2 is a partially enlarged cross-sectional view where a vicinity ofa separation cell of the A-A′ cross section in FIG. 1 was enlarged.

FIG. 3 is a schematic view showing an end face of the porous body.

FIG. 4A is a schematic view showing a cross section parallel to the cellextension direction of the ceramic separation-membrane structure andshowing an embodiment where the ceramic separation-membrane structure isput in a housing.

FIG. 4B is a schematic view showing a cross section parallel to the cellextension direction of the ceramic separation-membrane structure andshowing another embodiment where the ceramic separation-membranestructure is put in a housing.

FIG. 5 is a schematic view showing a state of pouring seeding slurry ina particle adhesion step.

FIG. 6 is a schematic view showing an embodiment of a membrane formationstep of forming a zeolite membrane on a porous body by hydrothermalsynthesis.

FIG. 7 is a perspective view showing another membrane of a ceramicseparation-membrane structure of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, embodiments of the present invention will be described withreferring to drawings. The present invention is not limited to thefollowing embodiments, and changes, modifications, and improvements maybe made as long as they do not deviate from the scope of the invention.

FIG. 1 shows an embodiment of a honeycomb-shaped ceramicseparation-membrane structure 1 of the present invention. FIG. 2 shows apartially enlarged cross-sectional view where a vicinity of a separationcell of the A-A′ cross section in FIG. 1 is enlarged. Thehoneycomb-shaped ceramic separation-membrane structure 1 (hereinbelowsometimes referred to simply as ceramic separation-membrane structure)is provided with a honeycomb-shaped base material 30, an intermediatelayer 31, and a separation layer 32 (In the present specification, thebase material 30 and the intermediate layer 31 are referred to as aceramic porous body 9).

The honeycomb-shaped ceramic separation-membrane structure 1 haspartition walls 3 of a ceramic porous body 9 (hereinbelow sometimesreferred to simply as porous body 9) having a large number of poresformed therein, and cells 4 to function as flow passages for a fluid areformed by the partition walls 3. In the intermediate layer 31, a largenumber of pores are formed, and the average pore size is small incomparison with the surface of the base material 30, and the layer isdisposed on the surface of the base material 30. At least a part of theceramic porous body 9 has a structure where the aggregate particles arebonded to one another by an inorganic bonding material component. Inother words, either the base material 30 or the intermediate layer 31(when there is a plurality of intermediate layers 31 as described later,one of the layers) may be self-sintered (without any inorganic bondingmaterial component). Since the base material 30 has a honeycomb shape,the membrane area per unit volume can be made large, and the treatingcapability can be raised.

The porous body 9 including the base material 30 and the intermediatelayer 31 has a circular columnar external shape and an outer peripheralface 6. It is further provided with a plurality of separation cells 4 apassing through from one end face 2 a to the other end face 2 b andformed in rows and a plurality of water collection cells 4 b formed inrows from one end face 2 a to the other end face 2 b. In the ceramicseparation-membrane structure 1, each of the separation cells 4 a andthe water collection cells 4 b has a circular cross-sectional shape.Though the apertures of both the end faces 2 a and 2 b of the separationcells 4 a are open (are left as apertures), the apertures of both theend faces 2 a and 2 b of the water collection cells 4 b are plugged withplugging members to form plugged portions 8; and discharge flow passages7 are provided in such a manner that the water collection cells 4 bcommunicate with the external space. In addition, a separation layer 32is disposed on the surface of the intermediate layer 31 of the insidewall face of each of the separation cells 4 a having a circularcross-sectional shape. On the other hand, the water collection cells 4 bare provided with neither the intermediate layer 31 nor the separationlayer 32. It is preferable that a glass seal 35 is disposed so as tocover at least the end faces 2 a, 2 b of the base material 30. Theceramic separation-membrane structure 1 is a ceramic filter forseparating a mixture.

In the ceramic separation-membrane structure 1, the internal pressurefracture strength fracturing the structure at the time that pressure isapplied to the inside of the separation cells 4 a is 7 MPa or more. Theinternal pressure fracture strength means pressure fracturing theceramic separation-membrane structure 1 by applying the pressure to theinside of the separation cells 4 a. Conventionally, there has been nohoneycomb-shaped ceramic separation-membrane structure having aninternal pressure fracture strength of 7 MPa or more. A ceramicseparation-membrane structure 1 of the present invention has higherinternal pressure fracture strength than a conventional one byspecifying the base material thickness 40, the intermediate layerthickness 41 (see FIG. 3), and the proportion of the inorganic bondingmaterial in the intermediate layer to be within predetermined ranges andthe like. Hereinbelow, description will be given in more detail.

(Base Material)

It is preferable that the base material 30 has an average pore size of 5to 25 μm. It is more preferably 6 to 20 μm. When the average pore sizeof the base material 30 is below 5 μm, the permeation rate of thepermeation separation component separated by the separation layer 32 atthe base material 30 becomes remarkably low, and the permeation flowrate per unit time may be reduced. On the other hand, when it is above25 μm, the separation layer 32 cannot be formed uniformly, and theseparation performance may be deteriorated.

In addition, it is preferable that the base material 30 has a porosityof 25 to 50%. The average pore size and the porosity are measured by amercury porosimeter.

The material for the base material 30 is ceramic. It is preferable thatthe aggregate particles are of alumina (Al₂O₃), titania (TiO₂), mullite(Al₂O₃.SiO₂), powder of potsherd, cordierite (Mg₂Al₄Si₅O₁₈), or thelike. Of these, alumina is further preferable in that a raw material(aggregate particles) having a controlled particle diameter can easilybe obtained, that stable kneaded material can be formed, and that it hashigh corrosion resistance. The inorganic bonding material is preferablyone selected from the group consisting of sinterable alumina, silica,glass frit, clay mineral, and sinterable cordierite. The inorganicbonding material is a bonding material for bonding the aggregateparticles to one another and an inorganic component which is sinteredand solidified at temperature where the aggregate component is notsintered. When alumina is selected as the aggregate component, theaverage particle diameter of the sinterable alumina is not larger thanone tenth of that of the aggregate. When cordierite is selected as theaggregate component, the average particle diameter of sinterablecordierite is not larger than one tenth of that of the aggregate.Incidentally, regardless of the base material 30, the intermediate layer31, or the like, the average particle diameter is measured by the “laserdiffraction method”. As the clay mineral, there can be mentioned kaolin,dolomite, montmorillonite, feldspar, calcite, talc, mica, and the like.

There is no particular limitation on the entire shape and size of thebase material 30 as long as they do not hinder the separation function.As the entire shape, there can be mentioned shapes of, for example, acircular column (circular cylinder), a quadrangular prism (cylinderhaving a quadrangular cross section perpendicular to the central axis),and a triangular prism (cylinder having a triangular cross sectionperpendicular to the central axis). Of these, a circular column ispreferable in that extrusion is easy, that firing deformation is little,and that sealing with the housing is easy. When it is used for precisefiltration or ultrafiltration, the shape is preferably a circular columnhaving a diameter of 30 to 220 mm in a cross section perpendicular tothe central axis, and a length of 150 to 2000 mm in the central axialdirection.

As the cross-sectional shape of the cells 4 (shape in a cross sectionperpendicular to the cell 4 extension direction) of the base material30, there can be mentioned, for example, a circle, an ellipse, and apolygon. As the polygon, a quadrangle, a pentagon, a hexagon, atriangle, and the like can be mentioned. Incidentally, the cell 4extension direction is the same as the central axial direction when thebase material 30 has a circular columnar (circular cylindrical) shape.

When the cross-sectional shape of the cells 4 of the base material 30 iscircular, the diameter of the cells 4 is preferably 1 to 5 mm. When itis smaller than 1 mm, the membrane area may become small. When it islarger than 5 mm, strength of the ceramic filter may be deteriorated.

In the base material 30, the base material thickness 40 excluding theintermediate layer 31 and the separation layer 32 at the shortestportion between the cells 4 is preferably 0.51 mm or more and 1.55 mm orless. The base material thickness 40 means thickness of the portionexcluding the intermediate layer 31 and the separation layer 32 at thetime that the base material 30 is formed by extrusion as shown in FIG.3. The base material thickness 40 is more preferably 0.51 mm or more and1.2 mm or less, furthermore preferably 0.65 mm or more and 1.0 mm orless. The base material thickness 40 of 0.51 mm or more enables toobtain sufficient internal pressure fracture strength. However, when thebase material thickness 40 is too large, the number of cells whichcapable of forming in the fixed volume is reduced, and therefore themembrane area becomes small. Since this lowers the permeation flow rate,it is preferably 1.55 mm or less. Incidentally, the base materialthickness 40 is the distance shown in FIG. 3 when the cells 4 arecircular whereas it is the shortest distance between cells 4 when thecells have another shape.

(Intermediate Layer)

As shown in FIG. 2, an intermediate layer 31 is disposed on the basematerial 30, and a separation layer 32 is disposed on a surface (insidewall faces of the separation cells 4 a) of the intermediate layer 31.Though only one intermediate layer 31 is sufficient for a ceramicseparation-membrane structure 1 of the present invention, the averagepore size of the intermediate layer 31 located as the lower layer underthe separation layer 32 is preferably 0.005 to 2 μm. It is morepreferably 0.05 μm or more and 1 μm or less, furthermore preferably 0.1μm or more and 0.5 μm or less. By specifying it to 0.005 μm or more,large pressure loss and reduction in permeation rate can be inhibited.By specifying it to 2 μm or less, the strength can be increased, along-term reliability as a ceramic separation-membrane structure 1 isenhanced, the separation layer thickness can be reduced for disposition,and the permeation rate can be increased.

When the intermediate layer 31 is constituted of a plurality of layers,it is preferable that the intermediate layers 31 are disposed in such amanner that the average pore size decreases in order from the basematerial 30 side to the separation layer 32 side. Specifically, it ispreferable that the intermediate layer 31 is constituted of the firstintermediate layer 31 a having an average pore size of 1 μm order andthe second intermediate layer 31 b having an average pore size of 0.1 μmorder.

The thickness of the intermediate layer 31 (the intermediate layerthickness 41) is preferably 150 μm or more and 500 μm or less. When theintermediate layer is constituted of a plurality of layers, theintermediate layer thickness 41 is total thickness of all the layers. Itis more preferably 160 μm or more and 400 μm or less, furthermorepreferably 200 μm or more and 300 μm or less.

It is preferable that the aggregate particles of the intermediate layer31 are one selected from the group consisting of alumina, titania,mullite, powder of potsherd, and cordierite. In addition, the inorganicbonding material of the intermediate layer 31 is preferably one selectedfrom the group consisting of sinterable alumina, silica, glass frit,clay mineral, and sinterable cordierite. The inorganic bonding materialis an inorganic component which is sintered and solidified attemperature where the aggregate component is not sintered. When aluminais selected as the aggregate component, the average particle diameter ofthe sinterable alumina is not larger than one tenth of that of theaggregate. When cordierite is selected as the aggregate component, theaverage particle diameter of sinterable cordierite is not larger thanone tenth of that of the aggregate. Incidentally, regardless of the basematerial 30, the intermediate layer 31, or the like, the averageparticle diameter is measured by the “laser diffraction method”. As theclay mineral, there can be mentioned kaolin, dolomite, montmorillonite,feldspar, calcite, talc, mica, and the like.

It is preferable that the proportion of the inorganic bonding materialcomponent in the inorganic solid content of the intermediate layer 31 is26% by mass or more and 42% by mass or less. It is more preferably 28%by mass or more and 42% by mass or less, furthermore preferably 30% bymass or more and 42% by mass or less. Incidentally, the proportion ofthe inorganic bonding material component in the inorganic solid content(mass %)=(inorganic bonding material)/(aggregate particles+inorganicbonding material)×100.

(Separation Layer)

The separation layer 32 has a plurality of pores formed therein, and theaverage pore size is small in comparison with the porous body 9 (thebase material 30 and the intermediate layer 31), and the layer 32 isdisposed on the wall faces (surfaces of the partition walls 3) insidethe cells 4. Since a ceramic filter thus having a structure providedwith a separation layer 32 exhibits a separation function exclusively bythe separation layer 32, the average pore size of the porous body 9 canbe made large. Therefore, the fluid-flow resistance at the time that thefluid having passed through the separation layer 32 and moved into theporous body 9 from the cells 4 passes through the inside of the porousbody 9 can be reduced, and the fluid permeability can be enhanced.

The average pore size of the separation layer 32 can appropriately bedetermined depending on the filtration performance or separationperformance required (depending on the particle size of the substance tobe removed). For example, in the case of a ceramic filter used forprecise filtration or ultrafiltration, it is preferably 0.01 to 1.0 μm.In this case, the average pore size of the separation layer 32 ismeasured by the air flow method described in ASTM F316.

As the separation layer 32, there can be employed a gas separationmembrane and a reverse osmosis membrane. There is no particularlimitation on the gas separation membrane, and it may suitably beselected according to the kind of gas to be separated, such as a knowncarbon monoxide separation membrane, helium separation membrane,hydrogen separation membrane, carbon membrane, zeolite membrane, silicamembrane, and titania UF membrane. As the separation membrane 32, therecan be mentioned, for example, the carbon monoxide separation membranedescribed in U.S. Pat. No. 4,006,107, the helium separation membranedescribed in U.S. Pat. No. 3,953,833, the hydrogen separation membranedescribed in U.S. Pat. No. 3,933,907, the carbon membrane described inJP-A-2003-286018, the DDR type zeolite membrane complex described inJP-A-2004-66188, and the silica membrane described in WO No.2008/050812.

When the separation layer 32 is a zeolite membrane, there can be used azeolite having a crystal structure of LTA, MFI, MOR, FER, FAU, or DDR asthe zeolite. When the separation layer 32 is a DDR type zeolite, it canbe used particularly as a gas separation membrane used for selectivelyseparating carbon dioxide.

(Plugged Portion)

The plugging member preferably contains aggregate particles, aninorganic bonding material, a binder, a thickener, and a water retentionagent. The plugging member can be formed with the same material as theporous body 9. It is preferable that the plugged portion 8 has aporosity of 25 to 50%. When the porosity of the plugged portion 8 isabove 50%, the solid content contained in the slurry for theintermediate layer used for forming the intermediate layer 31 may passthrough the plugged portion 8. On the other hand, when the porosity ofthe plugged portion 8 is below 20%, discharge of the water contentcontained in the slurry for the intermediate layer used for forming theintermediate layer 31 may be difficult.

(Glass Seal)

In a ceramic separation-membrane structure 1 of the present invention,it is preferable to further provide a glass seal 35 so as to cover theporous body on the side, from which a mixed fluid flows therein, of theend face 2 of the ceramic separation-membrane structure 1 in order tosuppress the mixed fluid containing a permeable separation componentfrom directly flowing in from the porous body portion at the end face 2of the ceramic separation-membrane structure 1 and flowing out withoutbeing separated by the separation layer 32 formed on the inside wallsurfaces of the predetermined separation cells 4 a.

The thickness of the glass seal 35 is preferably 30 to 500 μm. When itis thicker than 30 μm, the durability is improved, and when it isthinner than 500 μm, a fluid can flow therein without being hinderedsince the glass seal 35 does not spread out into the cells 4. When theglass seal 35 is thick, the ceramic filter may be heavy.

Though the material of the glass seal 35 is not particularly limited aslong as it is glass which can be used as a seal material for a watertreatment filter, alkali-free glass is preferable. By forming the glassseal 35 with alkali-free glass, the movement of alkali components fromthe glass seal 35 can be inhibited almost completely. Therefore, itinhibits condensation of alkali components derived from the glass seal35 at the interface between the base material 30 or the separation layer32 and the glass seal 35, and the corrosion resistance of the ceramicseparation-membrane structure 1 can be improved dramatically. Therefore,corrosion of the base material 30 or the separation layer 32 in thevicinity of the glass seal 35 can be inhibited effectively, and thestructure exhibits excellent corrosion resistance capable of withstandchemical washing many times.

(Separation Method)

Next, there is described a method for separating some of the componentsfrom the mixture of several kinds of fluids by the use of the ceramicseparation-membrane structure 1 of the present embodiment. As shown inFIG. 4A, when the fluid is separated by the use of the honeycomb-shapedceramic separation-membrane structure 1 of the present embodiment, it ispreferable that the ceramic separation-membrane structure 1 is put in acylindrical housing 51 having a fluid inflow port 52 and a fluid outflowport 53, that the target fluid F1 to be treated which is allowed to flowin from the fluid inlet port 52 of the housing 51 is separated by theceramic separation-membrane structure 1, and the separated treated fluid(treated fluid F2) is discharged from the fluid outflow port 53.

When the ceramic separation-membrane structure 1 is put in the housing51, it is preferable that the gap between the ceramicseparation-membrane structure 1 and the housing 51 is sealed with theseal material 54, 54 at both the end portions of the ceramicseparation-membrane structure 1 as shown in FIG. 4A.

All the target fluid F1 having flowed into the housing 51 from the fluidinflow port 52 flows into the cells 4 of the ceramic separation-membranestructure 1, and the target fluid F1 having flowed into the cells 4passes through the separation layer 32 and enters the base material 30as the treated fluid F2. Then, it flows out of the base material 30 fromthe outer peripheral face 6 of the base material 30 and is dischargedoutside (into the external space) from the fluid outflow port 53. Theseal material 54, 54 can inhibit the target fluid F1 from being mixedwith the treated fluid F2.

Though there is no particular limitation on the material for the housing51, for example, stainless steel can be mentioned. Though there is noparticular limitation on the seal material 54, for example, an O-ringcan be mentioned. As the material for the seal material 54, fluorinerubber, silicone rubber, ethylene, and propylene rubber can bementioned. These materials are suitable for the use at high temperaturefor a long period of time.

FIG. 4B shows another embodiment where the ceramic separation-membranestructure 1 is put in the housing 51. As shown in FIG. 4B, the ceramicseparation-membrane structure 1 is put in the cylindrical housing 51having the fluid inflow port 52 and the fluid outflow ports 53, 58. Inthe embodiment, the target fluid F1 allowed to flow in from the fluidinflow port 52 of the housing 51 is separated by the ceramicseparation-membrane structure 1, the separated target fluid (treatedfluid F2) is discharged from the fluid outflow port 53, and the rest(fluid F3) can be discharged from the fluid outflow port 58. Since thefluid F3 can be discharged from the fluid outflow port 58, flow rate ofthe target fluid F1 can be raised during the operation, and thepermeation rate of the treated fluid F2 can be raised. Generallyspeaking, the permeation amount of the treated fluid F2 of the filterdrops since a sedimentary layer of unfiltered component s is formed onthe membrane surface. Even in gas separation, the permeation amount ofthe treated fluid F2 falls by concentration polarization where theconcentration of the components which do not pass through the membraneincreases. However, when the flow rate of the target fluid F1 is high,since unfiltered components flow to the fluid outflow port 58, theformation of the sedimentary layer and the concentration polarizationare reduced, and clogging is hardly caused.

(Preparation Method)

Next, the preparation method of a ceramic separation-membrane structure1 according to the present invention will be described. In the firstplace, a raw material for the porous body is formed. For example,extrusion is performed by the use of a vacuum extruder. This enables toobtain a honeycomb-shaped unfired base material 30 having separationcells 4 a and water collection cells 4 b. There are other methods suchas press forming and casting, and the method can appropriately beselected.

Then, in the unfired base material 30 obtained above, discharge flowpassages 7 communicating from one portion of the outer peripheral face 6to another portion bypassing through the water collection cells 4 b areformed. The discharge flow passages 7 can be formed, for example, bymachining grooves on the outer peripheral face 6, breaking with agrinding stone or the like, and then breaking through the watercollection cells 4 b with a jig having an acute angle.

Next, plugging members in a slurried state are filled into the spacesfrom both the end faces 2 a, 2 b of the water collection cells 4 b tillthey reach the discharge flow passages 7 of the unfired base material 30with the discharge flow passages 7 obtained above. Specifically, a film(masking) of polyester or the like is attached to both the end faces 2a, 2 b of the base material 30, and holes are made in portionscorresponding to the specific separation cells 4 a. Then, the end faces2 a, 2 b provided with a film of the base material 30 are pressedagainst the inside of the container filled with the plugging member(slurry), and a pressure of, for example, 200 kg is further applied withan air cylinder or the like for the filling. Subsequently, the unfiredbase material 30 having plugging members obtained above is fired at, forexample, 900 to 1400° C.

Then, on the inside wall faces of the separation cells 4 a of the basematerial 30, a plurality of intermediate layers 31 functioning as a basefor the separation layer 32 is formed. In the first place, slurry forthe intermediate layers is prepared in order to form the intermediatelayers 31 (form membranes). The slurry for the intermediate layers canbe prepared by adding water to a ceramic raw material of alumina,mullite, titania, cordierite, or the like having a desired particlediameter (e.g., average particle diameter of 3.2 μm) of the samematerial as the base material 30. To the slurry for the intermediatelayers, an inorganic bonding material is added in order to enhance themembrane strength after sintering. For the inorganic bonding material,there can be used clay, kaolin, titania sol, silica sol, glass frit, orthe like. After the slurry for the intermediate layers is allowed toadhere to the inside wall faces of the separation cells 4 a (by the useof, for example, a device disclosed in JP-A-61-238315), it is dried andsintered at, for example, 900 to 1050° C. to form the intermediatelayers 31.

The intermediate layers 31 can be formed independently with plural kindsof slurry having varied average particle diameters. By disposing thesecond intermediate layer 31 b on the first intermediate layer 31 a, theinfluence of the unevenness of the surface of the porous body 9 can bereduced. As a result, even if the separation layer 32 is made thin,defects as the ceramic separation-membrane structure 1 can be reduced.That is, there can be obtained a ceramic separation-membrane structure 1where a separation layer 32 having high flux, low cost, and highseparation performance is disposed.

Next, the separation layer 32 is formed on the intermediate layer 31.The case of disposing a zeolite membrane as the separation layer 32 willbe described. The zeolite membrane-forming method includes a particleadhesion step where zeolite particles are allowed to adhere to theporous body 9 by allowing slurry having zeolite particles serving asseeds dispersed therein to flow down by its own weight along the surfaceof the porous body 9 and a membrane-forming step where a zeolitemembrane is formed on the porous body 9 by hydrothermal synthesis withimmersing the porous body 9 having the zeolite particles adheringthereto in a sol. The flowing down in the particle adhesion step meansthat the slurry flows down on the surface of the porous body 9 byallowing the slurry to drop one by one freely by its own weight on theporous body 9. In the flow-down method, a large amount of liquid isallowed to flow in parallel with the surface by, for example, pouringslurry into holes of the porous body 9 having circular cylindricalholes. This allows the slurry poured to flow along the surface of theporous body 9 by its own weight. Therefore, penetrating into the porousbody 9 is little. On the other hand, the conventionally knownfalling-drop method is a method of allowing a small amount of slurry tofall perpendicularly from above a flat plate, and the slurry fallingdown penetrates into the flat plate by its own weight. Therefore, themembrane becomes thick.

[1] Preparation of Slurry for Seeding and Seeding (Particle AdhesionStep)

A DDR type zeolite crystal powder is produced, and it is used as a seedcrystal as it is or by being pulverized as necessary. The DDR typezeolite powder (serving as the seed crystal) is dispersed in a solventto obtain slurry 64 (slurry for seeding). It is preferable to dilute theslurry for seeding by a solvent so that the concentration of the solidcontent contained therein becomes 1% by mass or less. As the solvent fordilution, water, ethanol, or ethanol aqueous solution is preferable. Asthe solvent used for the dilution, there may be used an organic solventsuch as acetone or IPA or an organic solvent aqueous solution besideswater or ethanol. Since the use of an organic solvent having highvolatility can reduce drying time and reduce penetrating of the slurry64 for seeding at the same time, a thinner zeolite membrane can beformed. Though a general stirring method can be employed as a method fordispersing the DDR type zeolite powder in the slurry, a method such as asupersonic wave treatment may be employed.

FIG. 5 shows one embodiment of seeding by a flow-down method (particleadhesion step). A porous body 9 is fixed to the lower end of awide-mouth funnel 62, and a cock 63 is opened to allow the seedingslurry 64 to flow in from above the porous body 9 and to pass throughthe cells 4, thereby performing the particle adhesion step.

The concentration of the solid content in the slurry 64 for seeding(particle adhesion step) is preferably within the range from 0.00001 to1% by mass, more preferably within the range from 0.0001 to 0.5% bymass, and furthermore preferably within the range from 0.0005 to 0.2% bymass. When the concentration is lower than the lower limit of the rangefor the concentration, the number of steps is increased to cause highcosts. In addition, when it is above 1% by mass, a thick zeoliteparticle layer is formed on the surface of the porous body 9, and thethick membrane causes low flux.

For the slurry 64 in the particle adhesion step, water can be used asthe solvent for dispersing the zeolite particles. An organic solvent oran organic solvent aqueous solution may be used. Further, ethanol, anethanol aqueous solution, or the like may be used. In particular, whenethanol having high volatility is used as the solvent, since the insideportion of the porous body 9 is pressurized by volatilized ethanol rightafter the flowing, the flowing liquid is pushed out to the surface ofthe porous body 9, and the amount of the penetrating of the slurry forseeding can be reduced.

It is preferable to perform the step of allowing the slurry 64containing zeolite particles as seeds to flow down in the particleadhesion step (FIG. 5) plural times. The plural times mean about 2 to 10times. The more times increase quantity of work and costs. The number oftimes is preferably up to about 8, more preferably about 2 to 6. Byperforming the step plural times, the zeolite particle can adhere to theentire surface of the porous body 9 evenly.

It is preferable that the preparation method of a zeolite membraneaccording to the present invention includes a step of allowing theslurry 64 containing zeolite particles to flow down with flipping theporous body 9 upside down after the slurry 64 containing zeoliteparticles serving as seeds is allowed to flow down. This enables toallow the zeolite particles to adhere to the surface of the porous body9 evenly and uniformly.

When the slurry 64 containing zeolite particles serving as seeds isallowed to flow down, it is desirable to perform masking with a sealtape or the like on the outer peripheral face 6 of the porous body 9.The masking enables to reduce the amount of penetrating of the slurry 64for seeding and to allow the zeolite particles to adhere more uniformly.By reducing the amount of seeping of the slurry 64 for penetrating, athinner zeolite membrane can be formed.

It is preferable that the manufacturing method of a zeolite membrane ofthe present invention includes a draught drying step after the slurry 64containing zeolite particles serving as seeds is allowed to flow down.The draught drying means drying the slurry 64 by sending wind to thesurface of the porous body 9 where the slurry 64 containing zeoliteparticles adheres. By performing the draught drying, the drying speed israised, and the zeolite particles easily move to the surface and gatheron the surface with the movement of the liquid at the time that theliquid evaporates.

In addition, the draught drying is preferably performed with humidifiedwind. By performing the draught drying with humidified wind, seeds canbe fixed more strongly on the porous body 9. By fixing the seedsstrongly on the porous body 9, detachment of the zeolite particles uponthe following hydrothermal synthesis can be inhibited, and a zeolitemembrane having less defects can be formed stably. Incidentally, thesame effect can be obtained by including an exposure step of laying theporous body 9 subjected to draught drying with wind not subjected tohumidification in water vapor after the flowing and seeding of theslurry 64.

[2] Preparation of Raw Material Solution (Sol)

Next, there is prepared a raw material solution having a predeterminedcomposition including 1-adamantanamine dissolved in ethylenediamine.

Since 1-adamantanamine is a SDA (structure defining agent) in synthesisof a DDR type zeolite, that is, a substance to serve as a template forforming a crystal structure of the DDR type zeolite, the molar ratio toSiO₂ (silica) which is a raw material for the DDR type zeolite isimportant. The molar ratio of 1-adamantanamine/SiO₂ is necessarilywithin the range from 0.002 to 0.5, preferably within the range from0.002 to 0.2, more preferably within the range from 0.002 to 0.03. Whenthe molar ratio of 1-adamantanamine/SiO₂ is below this range,1-adamantanamine of the SDA is insufficient, and therefore it isdifficult to form a DDR type zeolite. On the other hand, when the molarratio is above this range, expensive 1-adamantanamine is added more thannecessary, which is not preferable from the viewpoint of productioncosts.

Since 1-adamantanamine is hardly soluble in water as a solvent forhydrothermal synthesis, it is subjected to preparation for a rawmaterial solution after dissolving it in ethylenediamine. By preparing araw material solution in a uniform condition with completely dissolving1-adamantanamine in ethylenediamine, it becomes possible to form DDRtype zeolite having a uniform crystal size. The molar ratio ofethylenediamine/1-adamantanamine is necessarily within the range from 4to 35, preferably within the range from 8 to 24, more preferably withinthe range from 10 to 20. When the molar ratio ofethylenediamine/1-adamantanamine is below this range, the amount isinsufficient for completely dissolving 1-adamantanamine. On the otherhand, when the molar ratio is above this range, the ethylenediamine isused more than necessary, which is not preferable from the viewpoint ofproduction costs.

According to the preparation method of the present invention, colloidalsilica is used as a silica source. Though a commercially availablecolloidal silica can suitably be used as the colloidal silica, thecolloidal silica can be prepared by dissolving minutely powdered silicain water or by subjecting alkoxide to hydrolysis.

The molar ratio of water contained in the raw material solution to SiO₂(silica) (water/SiO₂ molar ratio) is necessarily within the range from10 to 500, preferably within the range from 14 to 250, and morepreferably within the range from 14 to 112. When the water/SiO₂ molarratio is below this range, it is not preferable in that a large amountof unreacted SiO₂ which is not crystallized remains because the SiO₂concentration of the raw material solution is too high. On the otherhand, when it is above this range, it is not preferable in that a DDRtype zeolite cannot be formed because the SiO₂ concentration of the rawmaterial solution is too low.

According to the preparation method of the present invention, besidesDDR type zeolite of all silica type, there can be manufactured DDR typezeolite containing aluminum and metal cation in the framework(hereinbelow referred to as “DDR type zeolite of low silica type”).Since the DDR type zeolite of low silica type has a cation in pores, itsadsorption performance and catalyst performance are different from thoseof DDR type zeolite of all silica type. In the case of manufacturing DDRtype zeolite of low silica type, a raw material solution is prepared byadding an aluminum source and a cation source besides water as thesolvent and colloidal silica as the silica source.

As the aluminum source, there can be used aluminum sulfate, sodiumaluminate, metal aluminum, or the like. The SiO₂/Al₂O₃ molar ratio inthe case of converting aluminum to its oxide is necessarily within therange from 50 to 1000, preferably within the range from 70 to 300, morepreferably within the range from 90 to 200. When the SiO₂/Al₂O₃ molarratio is below this range, it is not preferable in that the proportionof amorphous SiO₂ other than DDR type zeolite increases. On the otherhand, when it is above this range, it is not preferable in that theproperties as DDR type zeolite of low silica type cannot be exhibiteddue to remarkable reduction of the amount of aluminum and cation thoughDDR type zeolite can be manufactured, which makes no difference fromzeolite of all silica type.

As the cation, there can be mentioned a cation of one of alkali metals,i.e., K, Na, Li, Rb, and Cs. As the cation source, if Na is taken forexample, there can be mentioned sodium hydroxide, sodium aluminate, andthe like. The X₂O/Al₂O₃ molar ratio in the case of converting alkalimetal as the oxide is necessary within the range from 1 to 25,preferably within the range from 3 to 20, and more preferably within therange from 6 to 15. When the X₂O/Al₂O₃ molar ratio is below this range,it is not preferable in that DDR type zeolite having the aimedSiO₂/Al₂O₃ molar ratio is hardly obtained. On the other hand, when it isabove this range, it is not preferable in that amorphous SiO₂ is mixedin the product.

Preparation of a raw material solution has been described above. As aparticularly preferable mode, there can be mentioned a method ofpreparing a raw material solution by mixing a solution where1-adamantanamine is dissolved in ethylenediamine, water as a solvent,and colloidal silica (in the case of synthesizing low silica type DDR,further aluminum sulfate as the aluminum source and sodium hydroxide thea cation source) at a predetermined ratio and dissolving them.

[3] Membrane Formation (Membrane Formation Step)

A container (e.g., a jar) containing the raw material solution is set ina homogenizer for agitation to obtain a sol 67 used for hydrothermalsynthesis. Next, as shown in FIG. 6, the porous body 9 subjected toseeding by the flow-down method is put in a pressure resistant container65, and, after the sol 67 prepared above is put therein, these are putin a drier 68 and subjected to a heating treatment (hydrothermalsynthesis) at 110 to 200° C. for 16 to 120 hours to obtain a zeolitemembrane.

The temperature of the heating treatment (synthesis temperature) ispreferably within the range from 110 to 200° C., more preferably 120 to180° C., and particularly preferably 120 to 170° C. When the temperatureof the heating treatment is below this range, it is not preferable inthat DDR type zeolite cannot be formed. On the other hand, when it isabove the range, it is not preferable in that unintended DOH typezeolite is formed due to phase transition.

Regarding the time for the heating treatment (synthesis time) in thepreparation method of the present invention, very short time of severalhours to five days is sufficient. In the preparation method of thepresent invention, since the DDR type zeolite powder is added to a basematerial by a flow-down method, crystallization of DDR type zeolite isfacilitated.

In the preparation method of the present invention, it is not necessaryto always stir the raw material solution (sol 67) during the heatingtreatment. This is because, since 1-adamantanamine to be contained inthe raw material solution is dissolved in ethylenediamine, the rawmaterial solution is maintained in a uniform state. Incidentally,whereas mixed crystals of DDR and DOH may be formed if the raw materialsolution is not always stirred in a conventional method, single-phasecrystals of DDR can be formed without forming DOH even if the rawmaterial solution is not always stirred according to the preparationmethod of the present invention.

[4] Washing and Removing Structure Defining Agent

Next, the porous body 9 having a zeolite membrane formed thereon iswashed with water or by boiling at 80 to 100° C., and then it is takenout and dried at 80 to 100° C. Then, the porous body 9 is put in anelectric furnace and heated at 400 to 800° C. for 1 to 200 hours in theambient atmosphere to remove 1-adamantanamine in the pores of thezeolite membrane by combustion. The above enables to form a thin anduniform zeolite membrane having a thickness of 10 μm or less and lessdefects than a conventional one.

The preparation method of a zeolite membrane of the present inventioncan be applied to zeolites having a crystal structure of LTA, MFI, MOR,FER, FAU, or DDR.

Next, there is described a case of disposing a silica membrane as aseparation layer 32 on the intermediate layer 31. The precursor solution(silica sol solution) to form a silica membrane can be prepared bysubjecting tetraethoxysilane to hydrolysis in the presence of nitricacid to obtain sol and diluting the sol with ethanol. In place ofdilution with ethanol, dilution with water is possible. By pouringprecursor solution (silica sol solution) to form a silica membrane fromabove the porous body 9 and passing it through the separation cells 4 aor by general dipping, the precursor solution is allowed to adhere tothe inside wall faces of the separation cells 4 a. Then, after thetemperature is raised at a rate of 100° C./hour and maintained at 500°C. for one hour, the temperature is lowered at 100° C./hour. Suchoperations of pouring, drying, raising temperature, and loweringtemperature are repeated 3 to 5 times to dispose a silica membrane. Asdescribed above, a ceramic separation-membrane structure 1 having asilica membrane as the separation layer 32 can be obtained.

Next, a description will be made regarding a case of disposing a carbonmembrane as the separation layer 32 on the intermediate layer 31. Inthis case, a membrane may be formed by bringing a precursor solutionwhich forms a carbon membrane into contact with the surface of theporous body 9 by means of dip coating, immersion, spin coating, spraycoating, or the like. The precursor solution can be obtained by mixingand dissolving a thermosetting resin such as phenol resin, melamineresin, urea resin, furan resin, polyimide resin, and epoxy resin; athermoplastic resin such as polyethylene; cellulose-based resin; orprecursor substances of these resins in an organic solvent such asmethanol, acetone, tetrahydrofuran, NMP, and toluene; water; or thelike. When a membrane is formed from the precursor solution, anappropriate thermal treatment may be performed according to the kind ofthe resin contained therein. The precursor membrane obtained in such amanner is carbonized to obtain a carbon membrane.

A description will be made regarding a case of disposing a titania UFmembrane as the separation layer 32 on the intermediate layer 31. In thefirst place, titanium isopropoxide is hydrolyzed in the presence of andnitric acid to obtain a titania sol solution. Then, the titania solsolution is diluted with water to obtain a sol solution for forming amembrane, and the sol solution is passed through the cells 4 to form atitania UF membrane in the cells 4.

Though there has been described an embodiment having plugged portions 8formed by plugging end faces 2 with plugging members, separation cells 4a, water collection cells 4 b, and discharge flow passages 7 as aceramic separation-membrane structure 1; as shown in FIG. 7, thestructure may have no plugging, be provided with a separation layer 32in all the cells 4 of the honeycomb-structured porous body 9 and with nowater collection cell 4 b and no discharge flow passage 7.

Example

Hereinbelow, the present invention will be described in more detail onthe basis of Examples. However, the present invention is not limited tothese Examples.

(Base Material)

A kneaded material was prepared by adding 20 parts by mass of aninorganic bonding material (sintering auxiliary) with respect to 100parts by mass of alumina particles (aggregate particles) having anaverage particle diameter of 50 μm, and water, a dispersant, and athickener were added to them, followed by mixing and kneading. Thekneaded material was extruded to manufacture a honeycomb-shaped unfiredbase material 30.

As the inorganic bonding material, there was used a material obtained bymelting a glass raw material containing SiO₂ (80 mol %), Al₂O₃ (10 mol%), and alkali earth (8 mol %) at 1600° C. for uniformalization; and,after it was cooled, it was pulverized to obtain an average particlediameter of 1 μm.

In the unfired base material 30, discharge flow passages 7 communicatingfrom one portion of the outer peripheral face 6 to another portion bypassing through the water collection cells 4 b were formed.

Next, slurried plugging member was filled in the spaces from both theend faces 2 a, 2 b till it reached the discharge flow passages 7 of thebase material 30. Then, the base material 30 was fired. The firingconditions were 1250° C. and one hour with both the temperature riserate and the temperature fall rate of 100° C./hour.

Next, the intermediate layer 31 of an alumina porous body having athickness of 150 μm and an average pore size of 0.5 μm was formed on thewall surfaces inside the cells 4 of the base material 30. The averagepore size was measured by the air flow method described in ASTM F316.

In the first place, slurry was prepared by adding 14 parts by mass of aninorganic bonding material to 100 parts by mass of alumina particles(aggregate particles) having an average particle diameter of 3.5 μm, andwater, a dispersant, and a thickener were further added to them,followed by mixing. Using the slurry, the slurry was allowed to adhereto the inner peripheral face of the base material 30 by the filtrationmembrane-forming method described in JP-B-63-66566. Then, firing wasperformed in an electric furnace in the ambient atmosphere to form thefirst intermediate layer 31 a. As the firing conditions, 950° C. for onehour was employed with both the temperature ascending rate and thetemperature descending rate of 100° C./hour. As the inorganic bondingmaterial, there was used a material obtained by melting a glass rawmaterial containing SiO₂ (77 mol %), ZrO₂ (10 mol %), Li₂O (3.5 mol %),Na₂O (4 mol %), K₂O (4 mol %), CaO (0.7 mol %), and MgO (0.8 mol %) at1600° C. for uniformalization; cooling it; and then pulverizing toobtain an average particle diameter of 1 μm.

Next, the second intermediate layer 31 b of a titania porous body havinga thickness of 15 μm and average pore size of 0.1 μm was formed on theinner peripheral wall (surface of the surface layer) of the porous body9. The average pore size was measured by the air flow method describedin ASTM F316.

The porous body 9 had a circular columnar external shape having an outerdiameter of 30 mm and a length of 160 mm. In Table 1, the base materialthickness 40, the intermediate layer thickness 41, and the cell diameter42 of the cells having a circular cross-sectional shape are shown,respectively.

(Forming of Glass Seal)

Next, a glass seal 35 was disposed on both the end faces 2 a, 2 b of thebase material 30 in the state that the aperture portions of the cells 4were not clogged. In the first place, slurry was prepared by addingalumina particles (ceramic particles), water, and an organic binder tothe inorganic bonding material as a raw material for the glass seal 35,followed by mixing. The portion of the alumina particles (ceramicparticles) in the mixture was 40% by mass with respect to the total massof the inorganic bonding material and the alumina particles. The portionof water in the mixture was 65 parts by mass when the total mass of theinorganic bonding material and the alumina particles was regarded as 100parts by mass, and the portion of the organic binder in the mixture was7 parts by mass when the total mass of the inorganic bonding materialand the alumina particles was regarded as 100 parts by mass. As theorganic binder, methyl cellulose was used. The slurry obtained above wasapplied to both the end faces 2 a, 2 b of the base material 30, followedby drying and firing to obtain the glass seals 35. The thickness of theglass seals 35 was 200 μm. The firing conditions were the same as thoseof the aforementioned preparing method of the intermediate layer 31. Theaverage particle diameter of the alumina particles (ceramic particles)in the glass seal 35 was 14 μm.

In addition, the inorganic bonding material used as the raw material forthe glass seals 35 was a material obtained by melting a glass rawmaterial containing SiO₂ (63 mol %), ZrO₂ (3 mol %), Al₂O₃ (5 mol %),CaO (9 mol %), BaO (17 mol %), and B₂O₃ (3 mol %) at 1600° C. forhomogenization; cooling it; and then pulverizing it to obtain an averageparticle diameter of 15 μm.

(Forming of DDR Membrane)

As the separation layer 32, a DDR membrane was formed on theintermediate layer 31.

(1) Preparation of Seed Crystal

A DDR type zeolite crystal powder was manufactured on the basis of themethod for preparing DDR type zeolite described in M. J. den Exter, J.C. Jansen, H. van Bekkum, Studies in Surface Science and Catalysis Vol.84, Ed. by J. Weitkamp et al., Elsevier (1994) 1159-1166 orJP-A-2004-083375. It was used as a seed crystal as it was or bypulverizing as necessary. After synthesis or after dispersing thepulverized seed crystal in water, coarse particles were removed toprepare a seed crystal dispersion liquid.

(2) Seeding (Particle Adhesion Step)

The seed crystal dispersion liquid prepared in (1) was diluted byion-exchanged water or ethanol, the DDR concentration was adjusted to be0.001 to 0.36% by mass (solid content concentration in slurry 64), andit was stirred with a stirrer at 300 rpm to obtain slurry for seeding(slurry 64). The porous body 9 was fixed to the lower end of awide-mouth funnel 62, and slurry for seeding of 160 ml was poured intothe porous body 9 from above and passed through the cells (see FIG. 5).At this time, after masking the outer peripheral face 6 of the porousbody 9 with a Teflon (registered trade mark), seeding was performed. Inthe porous body 9 where the slurry 64 was poured, the insides of thecells were subjected to draught drying at room temperature or at 80° C.at a wind speed of 3 to 6 m/s for 10 to 30 minutes. Pouring of theslurry 64 and the draught drying were repeated 1 to 6 times to obtain asample. After the drying, microstructure observation with an electronmicroscope was performed. Adhesion of DDR particles to the surface ofthe porous body 9 was confirmed.

(3) Membrane Formation (Membrane Formation Step)

After putting 7.35 g of ethylenediamine (produced by Wako Pure ChemicalIndustries, Ltd.) in a 100 ml fluorine resin jar, 1.156 g of1-adamantanamine (produced by Sigma-Aldrich Japan Co.) was added theretoand dissolved so that no precipitation of 1-adamantanamine might remain.In another container, 98.0 g of 30% by mass of colloidal silica (SnowtexS produced by Nissan Chemical Industries, Ltd.) and 116.55 g ofion-exchanged water were put, and they were slightly stirred. Then, themixture was put in the jar containing the mixed ethylenediamine and1-adamantanamine and strongly shaken to prepare a raw material solution.Molar ratios of components in the raw material solution were1-adamantanamine/SiO₂=0.016, water/SiO₂=21). Then, the jar containingthe raw material solution was set in a homogenizer, and stirring wasperformed for one hour. The porous body 9 having DDR particles adheringthereto obtained in (2) was disposed in a stainless steel pressureresistant container 65 provided with a fluorine resin internal cylinderhaving an internal capacity of 300 ml, and the raw material solution(sol 67) prepared above was put therein to perform a heating treatment(hydrothermal synthesis) at 140° C. for 50 hours (see FIG. 6). Uponhydrothermal synthesis, it was alkaline due to colloidal silica andethylenediamine of the raw material. A fracture cross section of theporous body 9 having membrane formed thereon was observed with ascanning electron microscope, and it was found that the thickness of theDDR membrane was 10 μm or less.

(4) Removal of Structure Defining Agent

The coated membrane was heated at 450 or 500° C. for 50 hours in theambient atmosphere in an electric furnace to remove 1-adamantanamine inthe pores by combustion. The crystal phase was identified by X-raydiffraction to confirm DDR type zeolite. In addition, after the membranewas formed, it was confirmed that the porous body 9 was covered with DDRtype zeolite.

(Forming of Titania UF Membrane)

As the separation layer, a titania UF membrane was formed on theintermediate layer 31. Titanium isopropoxide was subjected to hydrolysisin the presence of nitric acid to obtain a titania sol solution. The solparticle diameter measured by a dynamic light-scattering method was 100nm.

The titania sol solution was diluted with water, and PVA as an organicbinder was appropriately added thereto to obtain a sol solution forforming a membrane. It was passed through the cells 4 to form a membranein the cells 4. After the sample was dried, it was thermally treated at500° C. to form a titania OF membrane.

(Forming of Silica Membrane)

As the separation layer, a silica membrane was formed on theintermediate layer 31. The precursor solution (silica sol solution) toform a silica membrane was prepared by subjecting tetraethoxysilane tohydrolysis in the presence of nitric acid to obtain a sol solution anddiluting the sol solution with ethanol. The precursor solution (silicasol solution) to form a silica membrane was poured from above the porousbody 9 having an intermediate layer formed thereon, and the solution waspassed through the separation cells 4 a to allow the precursor solutionto adhere to the inside wall faces of the separation cells 4 a. Then,temperature was raised at 100° C./hour, and, after the temperature wasmaintained at 500° C. for one hour, the temperature was lowered at 100°C./hour. Such operations of pouring, drying, raising temperature, andlowering temperature were repeated 3 to 5 times to dispose a silicamembrane.

(Forming of Carbon Membrane)

As the separation layer, a carbon membrane was formed on an intermediatelayer 31. A precursor solution was obtained by mixing and dissolving aphenol resin in an organic solvent. The precursor solution to form acarbon membrane was brought into contact with the surface of the porousbody 9 by dip coating to form a carbon membrane.

As shown in FIG. 4A, the ceramic separation-membrane structure 1 was putin a cylindrical housing 51 having a fluid inflow port 52 and a fluidoutflow port 53, and pressure was applied by water by allowing the waterto flow in from the fluid inlet port 52 of the housing 51 to examine thestrength with which the ceramic separation-membrane structure 1 wasfractured. When the pressure was not raised because of water permeation,water permeation was blocked by coating natural latex rubber on theinside faces of the cells 4 and drying it to measure the internalpressure fracture strength.

TABLE 1 Proportion of Base material Intermediate inorganic Internalpressure thickness layer thickness bonding material Cell diameterfracture strength Material for mm mm mass % mm MPa separation layerComp. Ex. 1 0.51 0.10 36 2.9 6.7 DDR membrane Example 1 0.51 0.15 36 2.88.8 DDR membrane Example 2 0.51 0.20 36 2.7 10.5 DDR membrane Example 30.51 0.25 36 2.6 11.3 DDR membrane Example 4 0.51 0.30 36 2.5 10.7 DDRmembrane Example 5 0.51 0.50 36 2.3 8.0 DDR membrane Comp. Ex. 2 0.510.60 36 2.0 6.8 DDR membrane Example 6 0.65 0.15 26 2.5 8.9 DDR membraneExample 7 0.65 0.15 26 2.5 8.8 Titania UF membrane Example 8 0.65 0.1526 2.5 8.8 Silica membrane Example 9 0.65 0.15 26 2.5 8.8 Carbonmembrane

Examples 1 to 5, Comparative Examples 1 and 2

In Comparative Example 1, the intermediate layer 31 had a thickness ofbelow 0.15 mm, whereas, in Comparative Example 2, the intermediate layer31 had a thickness of above 0.5 mm, and the internal pressure fracturestrength was below 7 MPa. On the other hand, in Examples 1 to 5, theintermediate layer 31 had a thickness of 0.15 mm to 0.5 mm, and theinternal pressure fracture strength was 7 MPa. It was found out that,when the intermediate layer 31 is not within the range from 0.15 mm to0.5 mm, sufficient internal pressure fracture strength cannot beobtained.

Example 6 to 9

Example 6 is a case of a DDR membrane, Example 7 is a case of a titaniaUF membrane, Example 8 is a case of a silica membrane, and Example 9 isa case of a carbon membrane. In any of the cases for the separationlayer 32, sufficient internal pressure fracture strength was obtained.

TABLE 2 Membrane area Proportion of (porous body: Base materialIntermediate inorganic Internal pressure outer diameter thickness layerthickness bonding material Cell diameter fracture strength Material forof 30 mm, length mm mm mass % mm MPa separation layer of 160 mm) cm²Example 1 0.51 0.15 36 2.8 8.8 DDR membrane 502 Example 10 0.65 0.15 362.5 11.3 DDR membrane 432 Example 11 1.55 0.15 36 2.3 17.5 DDR membrane246

Example 1, 10, and 11

The base material thickness 40 of the base materials 30 was varied. Dueto the base material thickness 40 of 0.51 mm or more, sufficientinternal pressure fracture strength was obtained. In addition, when itwas 0.65 mm or more, more sufficient internal pressure fracture strengthwas obtained. However, when the base material thickness 40 is too large,since the number of cells capable of being disposed in a certain volumeis reduced, the membrane area is reduced. Since this lowers thepermeation flow amount, it was preferably 1.55 mm or less.

TABLE 3 Proportion of Base material Intermediate inorganic Internalpressure thickness layer thickness bonding material Cell diameterfracture strength Material for mm mm mass % mm MPa separation layerExample 6 0.65 0.15 26 2.5 8.9 DDR membrane Example 12 0.65 0.15 28 2.59.8 DDR membrane Example 10 0.65 0.15 36 2.5 11.3 DDR membrane Example13 0.65 0.15 42 2.5 10.9 DDR membrane

Examples 6, 10, 12, 13

The proportion of the inorganic bonding material component was varied.Sufficient internal pressure fracture strength was obtained due to aproportion of the inorganic bonding material component of 30% by mass ormore and 42% by mass or less. When the proportion of the inorganicbonding material was large, the separation layer 32 was hardly formed.In the case of a DDR type zeolite, since a seed crystal hardly adheresto the surface, a DDR type zeolite membrane was hardly formed.

INDUSTRIAL APPLICABILITY

A ceramic separation-membrane structure of the present invention cansuitably be used as a means for separating part of components from amixed fluid.

DESCRIPTION OF REFERENCE NUMERALS

1: ceramic separation-membrane structure, 2, 2 a, 2 b: end face, 3:partition wall, 4: cell, 4 a: separation cell, 4 b: water collectioncell, 6: outer peripheral face, 7: discharge flow passage, 8: pluggedportion, 9: porous body, 30: base material, 31: intermediate layer, 31a: first intermediate layer, 31 b: second intermediate layer, 32:separation layer, 35: glass seal, 40: base material thickness, 41:intermediate layer thickness, 42: cell diameter, 51: housing, 52: fluidinflow port, 53, 58: fluid outflow port, 54: seal material, 62:wide-mouth funnel, 63: cock, 64: slurry, 65: pressure resistantcontainer, 67: sol, 68: drier

1. A honeycomb-shaped ceramic separation-membrane structure comprising:a honeycomb-shaped base material having partition walls of a ceramicporous body having a large number of pores formed therein and aplurality of cells formed by the partition walls and functioning aspassages for a fluid passing through the ceramic porous body, anintermediate layer of a ceramic porous body having a large number ofpores having a small average pore diameter in comparison with a surfaceof the base material and being disposed on the surface of the basematerial, and a separation layer disposed on a surface of theintermediate layer; wherein at least a part of the base material and theintermediate layer has a structure where aggregate particles are bondedto one another by an inorganic bonding material component, and aninternal pressure fracture strength when pressure is applied to theinside of the cells is 7 MPa or more.
 2. The honeycomb-shaped ceramicseparation-membrane structure according to claim 1, wherein theintermediate layer thickness, which is the thickness of the intermediatelayer, is 150 μm or more and 500 μm or less.
 3. The honeycomb-shapedceramic separation-membrane structure according to claim 1, wherein thebase material thickness excluding the intermediate layer and theseparation layer at the shortest portion between the cells is 0.51 mm ormore and 1.55 mm or less.
 4. The honeycomb-shaped ceramicseparation-membrane structure according to claim 2, wherein the basematerial thickness excluding the intermediate layer and the separationlayer at the shortest portion between the cells is 0.51 mm or more and1.55 mm or less.
 5. The honeycomb-shaped ceramic separation-membranestructure according to claim 1, wherein the proportion of an inorganicbonding material component in an inorganic solid content of theintermediate layer is 26% by mass or more and 42% by mass or less. 6.The honeycomb-shaped ceramic separation-membrane structure according toclaim 2, wherein the proportion of an inorganic bonding materialcomponent in an inorganic solid content of the intermediate layer is 26%by mass or more and 42% by mass or less.
 7. The honeycomb-shaped ceramicseparation-membrane structure according to claim 3, wherein theproportion of an inorganic bonding material component in an inorganicsolid content of the intermediate layer is 26% by mass or more and 42%by mass or less.
 8. The honeycomb-shaped ceramic separation-membranestructure according to claim 4, wherein the proportion of an inorganicbonding material component in an inorganic solid content of theintermediate layer is 26% by mass or more and 42% by mass or less. 9.The honeycomb-shaped ceramic separation-membrane structure according toclaim 1, wherein the aggregate particles of the base material and theintermediate layer are one selected from the group consisting ofalumina, titania, mullite, powder of potsherd, and cordierite, and theinorganic bonding material of the base material and the intermediatelayer is one selected from the group consisting of sinterable alumina,silica, glass frit, clay mineral, and sinterable cordierite.
 10. Thehoneycomb-shaped ceramic separation-membrane structure according toclaim 1, wherein the base material has an average pore size of 5 to 25μm, and the intermediate layer has an average pore size of 0.005 to 2μm.
 11. The honeycomb-shaped ceramic separation-membrane structureaccording to claim 1, which is a gas separation membrane used for gasseparation.
 12. The honeycomb-shaped ceramic separation-membranestructure according to claim 1, wherein the separation layer is formedof zeolite.
 13. The honeycomb-shaped ceramic separation-membranestructure according to claim 12, wherein the separation layer is formedof DDR type zeolite.
 14. The honeycomb-shaped ceramicseparation-membrane structure according to claim 13, which is a gasseparation membrane used for selectively separating carbon dioxide.